ngrep strives to provide most of GNU grep's common features,
applying them to the network layer. ngrep is a pcap-aware tool that
will allow you to specify extended regular expressions to match
against data payloads of packets. It currently recognizes TCP and
UDP across ethernet, ppp and slip interfaces, and understands bpf
filter logic in the same fashion as more common packet sniffing
tools, like tcpdump and snoop.
